Answer:
Step-by-step explanation:
Given that PRST is a parallelogram
Also given that a side RS is perpendicular to ST
This implies by parallel lines property that interior angles are supplementary
Hence angle T=angle S=angle P= angle R =90 degrees
This makes PQRS a rectangle since each angle is 90 degrees
Now another is given as RPS angle =45
If RPS =45, then since PRS is a right triangle, other angle PSR =45
Or PRS is isosceles triangle with PR =RS
Now we find that in the rectangle PRST, adjacent sides are equal
Hence PRST is nothing but a square
since
i) each angle is 90
ii) adjacent sides are equal
, 
and the solutions are decreasing functions.